Tony Stewart has broken his silence after causing the death of 20-year-old Kevin Ward JR at a night race in New York on Saturday.

Witnesses have reported that veteran driver Stewart hit young racer Kevin Ward Jr, who was walking on the track after they collided on a prior lap at the Empire Super Sprints in Canandaigua, New York.

On Sunday, the three-time NASCAR champ issued a statement expressing his condolences to Ward Jr's family.

WARNING GRAPHIC VIDEO

Sorry: Tony Stewart has issued a statement revealing that 'there aren't words to describe the sadness' he feels after he caused the death of Kevin Ward Jr by running over and killing him in New York on Saturday

Tragedy: A driver died after being struck by a NASCAR star's car following a collision in New York

Crash: Wreckage from the race car of Michael McDowell (95) protrudes through the catch fence

Too young: Kevin Ward Jr (right) was pronounced dead after being struck by Stewart's sprint car at the Empire Super Sprints late Saturday night in Canandaigua, New York

Racer: Sprint car driver Kevin Ward Jr. was killed after he was run over by Tony Stewart on Saturday

'There aren't words to describe the sadness I feel about the accident that took the life of Kevin Ward Jr. It's a very emotional time for all involved, and it is the reason I've decided not to participate in today's race at Watkins Glen. My thoughts and prayers are with his family, friends and everyone affected by this tragedy,' Stewart said in a statement released by spokesman Mike Arning.

The competition director of Stewart's racing team said earlier in the day that he planned to continue Sunday's race, but he was later replaced by fellow driver Regan Smith.

A video purporting to be of the incident was posted on YouTube early Sunday and appeared to show Stewart spinning Ward Jr's car.

Talent: Kevin Ward Jr was just 20 years old and was a promising racing driver on the US circuit

The race was then put in 'caution' mode, with a yellow flag that warns the drivers to slow down.

A
driver, believed to be Ward, is seen exiting his crashed vehicle and
gesticulating at the other racers as they pass him. The racer then steps
into the oncoming traffic before he is suddenly struck and thrown into
the air.

In the next scene emergency workers are seen rushing to his aid. Ward Jr was apparently not struck at racing speed, but sprint cars can go as fast at 140 mph.

The
track canceled the remainder of the Empire Super Sprints slate within
five minutes while the Ontario County Sheriff's Department says its
officers are at the track investigating but do not see it as a criminal
matter.

Ontario County Sheriff Philip Povero said Stewart was 'visibly shaken' and had been cooperative in the investigation. Authorities were asking spectators and others to turn over any video they recorded of the crash.

'This is right now being investigated as an on-track crash and I don't want to infer that there are criminal charges pending,' Povero said. 'When the investigation is completed, we will sit down with the district attorney and review it. But I want to make it very clear: there are no criminal charges pending at this time.'

Dangerous: Spectator video shows the tragic moment Kevin Ward Jr (pictured) was hit by NASCAR driver Tony Stewart while angrily approaching him after the champ spun him around on the track.

Pointing fingers: Ward Jr was spun around by Stewart on the first lap, and he is then seen getting out of the car and approaching Stewart on foot as he comes around for another turn

'The prior lap, Tony had gotten into him – just spun him, nothing big, just spun him around. The caution came out. He hopped out of the car – the driver of the 13 [Kevin Ward] ... he hopped out to go and yell and point a finger at Tony, typical thing.'

'Tony came around ... the back end slid out, and he definitely caught him – I couldn't tell if it was with the front or the back of the car. ... The body made contact with the car and went sliding across the track a long distance, at least 50 feet. It was the worst thing I've ever seen.'

Ward Jr pictured with a woman who appears to be his girlfriend in a photo posted to his Facebook

Aftermath: A video of the incident showed Ward Jr flung 50ft down the track after the collision

Tributes: Flowers are placed at the entrance of the Canandaigua Motorsports Park

Help: An ambulance is pictured parked on the infield of Canandaigua Motorsports Park on Sunday

A spokesman for Stewart's racing team called Ward's death a 'tragic accident.'

'Our thoughts and prayers go out to his family and friends,' the spokesman said in a statement. 'We're still attempting to sort through all the details.'

According to his website Kevin Ward Jr has been racing since age four when he first started go-karting. He started Sprint Car racing in 2011. The 20-year-old from Port Leyden, New York, was Empire Super Sprint rookie of the year in 2012 and this year was his fifth season racing the Empire Super Sprints.